Magnetoresistive (MR) technology can be utilized in a variety of commercial, consumer, and industrial detection applications. Anisotropic magnetoresistive (AMR) properties of a material relate generally to the dependence of electrical resistance at the angle between the direction of electrical current and orientation of magnetic field is observed. AMR array position sensors yield a very accurate signal with respect to the position of a magnet. In conventional MR systems, a device can be provided for determining the position of a member movable along a path. In such a device, a magnet can be attached to the movable member and an array of AMR sensors are located adjacent the path. As the magnet approaches, passes, and moves away from a sensor, the sensor provides a varying output signal, which can be represented by a single characteristic curve that is representative of any of the sensors.
To determine the position of the movable member, the sensors are electronically scanned and data can be selected from a group of sensors having an output that indicates relative proximity to the magnet. A curve-fitting algorithm can then be utilized to determine a best fit of the data to the characteristic curve. The position of the magnet and, therefore, the movable member may be determined by placing the characteristic curve along a position axis.
In another conventional MR device, a position determining apparatus can be implemented, which includes a magnet that is attached to a movable member that moves along a predefined path of finite length. An array of sensors can be located adjacent to the predefined path. The transducers can provide an output signal as the magnet approaches, passes, and moves away from each transducer. A correction mechanism can also be implemented to correct for residual error caused by the non-linearity of the transducers. Such a correction mechanism preferably approximates the residual error with a predetermined function and applies correction factors that correspond to the predetermined function to offset the residual error. By correcting for the non-linearity of the transducers, the length of the magnet may be reduced and/or the spacing of the transducers may be reduced which, in turn, changes the signals generated from the AMR sensors respect of position.
Referring to FIGS. 1A and 1B, a prior art AMR array magnetic sensing system 100 and 150 are illustrated. The AMR array magnetic sensing system 100 and 150 generally includes a magnet 110 and an AMR array sensor 130 to sense the relative position of the magnet 110 within the array of AMR sensors 130. The magnet 110 must be positioned such that the magnetic flux lines 120 of the magnet 110 are in the same plane of the AMR array sensor 130. The magnet 110 generates magnetic flux lines 120 while moving in the direction as indicated by the arrow 140. If the air gap between the magnet 110 and AMR array sensor 130 is changed significantly according to the position of the magnet 110, the performance of the AMR array sensor 130 is reduced. FIG. 1B illustrates the different direction of the magnetic flux lines 120 wherein the magnet still moves in the same direction 140 with respect to the AMR array sensor 130. A signal can be generated as the magnet 110 moves and passes through the AMR array sensor 130. The position at which the magnetic flux lines are parallel or perpendicular to the AMR sensor runners 135 changes with respect to the air gap changes which, in turn, changes the signal generated from the AMR array sensors 130 despite the magnet not moving in direction 140.
The problem associated with such prior art AMR array magnetic device 100 and 150 is that as the distance between the AMR array sensor 130 and the magnet 110 changes, the signal changes decreasing repeatability of the sensor. As shown in FIG. 2, another prior art AMR array magnetic sensing system 200 have attempted to solve such problem by utilizing the magnet carrier 210 holding two magnets 220. The magnet carrier 210 can be placed over the AMR array sensors 240 and made to travel along the direction 250. The magnet carrier 210 can then be passed over the AMR array sensors 240 which comprise AMR runners 245 to produce less variable magnetic flux lines 230 with respect to air gap.
A problem associated with such approach is that the system 200 is sensitive to variation in directions other than the sensed direction. For example, the system 200 is susceptible to variation in ‘x’ direction although air gap variation in ‘z’ direction is virtually undetectable and the position of the magnet carrier in ‘y’ direction is still quantifiable. Consequently, positional information in ‘y’ direction (sensed direction) changes with variation in the ‘x’ direction, which is not desirable. Hence, the overall performance and the sensor-to-magnetic carrier tolerance of such prior art AMR array sensor decreases. It is, therefore, believed that a solution to the problems associated with such prior art sensor devices is the design and configuration of an improved AMR array magnetic design for improved sensor-to-magnet carrier tolerances, as described in greater detail herein.